ASCE 7-16 Service wind loads for Category IV Building

[Robcat71]

I am trying to determine if utilizing the 70% or 0.7 x 0.6W = 0.42 applies when I am designing a category IV building with an ultimate design wind speed of 125 mph. That corresponds to an MRI of 3,000. So in order to determine the wind service loads from the 10 year MRI or 25 year MRI from the commentary, is there an additional conversion needed or can you take directly the ratio of the squares, ex. 75^2/125^2 = 0.36 to check at a 10 year MRI?

Thanks in advance!

 

[phamENG]

Be careful with this one. A category IV building needs special consideration for what "service level" winds will be. What is the building? Is it a level one trauma center? The emergency response coordination headquarters for the region? If so, "service level" may need to be strength level to ensure that it will be fully functional during a design event.

We allow things like houses and shopping centers to have much lower service level wind loads because, in the event of the "big one" the only concern is that the building not collapse on anyone inside. There is an inherent expectation that the building doesn't need to be usable after the event, so long as it doesn't fall and hurt or kill anyone. Significant repairs and/or demolition and rebuilding will be necessary. For critical infrastructure and facilities, the standard may be different. It may be that it just needs to survive but can be repaired - in which case lowering the wind load for service checks may be appropriate. But if it's a critical facility that needs to remain operational during and after the event with little to no interruption, you need to assign a higher "service" level.

 

[Robcat71]

Thanks phamENG. It is a hospital and we are currently just checking the deflections utilizing 70% of the service load. Which is a 0.42 factor for the ultimate design wind pressure. We are holding it to a more conservative drift limit of H/500, although the façade could handle H/400. I am going to do some more research on this, and I appreciate your input. Hope to hear what others have to contribute based on their experiences as well.

 

[phamENG]

You're most welcome. You may want to flag your post, and in the report ask the moderators to move this to the Structural Engineering General forum. I don't think that many people watch this one, but there's a ton of activity from some really knowledgeable folks over there.

 

[r13]

Wasn't this already in the structural engineering forum? Now you have duplicate posts with a slight change on subject.

 

[r13]

This thread maybe helpful, though the discussion wasn't focused on Category IV buildings. But note that strength requirement might affect the decision on use of service level load. Link